1. Field of the Invention
The present invention relates to a video camera having an automatic focusing system for automatically focusing an image of an object to be photographed into an optimum focused condition.
2. Description of the Prior Art
Methods have already been proposed and practised for making automatic focusing (autofocus) which is an important function of a video camera. Among them is included a so-called "in-focus control method" which utilizes a video signal in a video camera. An example is reported in detail in an article entitled "Automatic Focusing in TV Camera using In-Focus Control Servo System" by Ishida et al., "NHK Technical Journal" Vol. 17, No. 1 (1965), p. 21.
In the "in-focus control method" mentioned above, a photographic lens is moved, and, on the basis of a change in level of a high frequency component of a certain frequency or higher contained in a video signal from an object (hereinafter referred to as "high frequency component"), a direction in which the photographic lens is to be moved for focusing (hereinafter referred to as "in-focus direction") and an in-focus position are detected. According to this method, as long as the photographic lens does not move, it is basically not clear in which direction, before or behind the present position, the in-focus position is present. Consequently, the photographic lens will often be moved in a defocusing direction at the time of start-up of the automatic focusing mechanism or upon movement of the object. This lowers the response speed of focusing operation extremely.